Conventionally, research of a lot of LED chip is conducted. The prior LED chip comprises a light emission layer, an anode electrode, and a cathode electrode. The light emission layer is made of nitride semiconductor material such as GaN, InGaN, AlGaN, and InAlGaN. The anode electrode is disposed on one surface in a thickness direction of the light emission layer, and the cathode electrode is disposed on the other surface in the thickness direction of the light emission layer. The LED chip is flip-chip mounted on the mounting substrate. In addition, the research of improving the light extraction efficiency of the LED chip is conducted. In order to improve the light extraction efficiency of the LED chip, the research and development of the LED chip having a structure which is designed so as not to prevent the anode electrode from being absorbed by the anode electrode is conducted. In order to improve the light extracting efficiency of the LED chip, the LED chip having a structure of preventing absorption of the light in the anode is researched and developed. The above mentioned LED chip is disclosed in patent literature 1 which is mentioned below.
The patent literature 1 discloses the LED chip which has a structure shown in FIG. 3. As will be understood from FIG. 3, LED chip comprises a light transmissive substrate 1, an n-type nitride semiconductor layer 2, a nitride light emission layer 3, a p-type nitride semiconductor layer 3; the light transmissive substrate 1 is made of sapphire substrate; the n-type nitride semiconductor layer 2, the nitride light emission layer 3, and the p-type nitride semiconductor layer 4 are located on one side surface of the light transmissive substrate 1. The anode electrode 7 is opposite of the nitride light emission layer 3 from the p-type nitride semiconductor layer 4. In addition, the cathode electrode 8 is located on the same side of the n-type nitride semiconductor layer 2 as the nitride light emission layer 3. Furthermore, the LED chip comprises a first transparent conductive film 9a, a second transparent conductive film 9b, a plurality of low refractive index dielectric layers 10P, a light reflective conductive film 11, and a barrier metal layer 14. The first transparent conductive film 9a, the second transparent conductive film 9b, a plurality of the low refractive index dielectric layers 10P, the light reflective conductive film 11, and the barrier metal layer 14 are interposed between the p-type nitride semiconductor layer 3 and the anode electrode 7. The first transparent conductive film 9a is formed on the p-type nitride semiconductor layer 4. The second transparent conductive film 9b is formed on the first transparent conductive film 9a. The low refractive index dielectric layers 10P are made of material which has a refractive index which is lower than a refractive index of the p-type nitride semiconductor layer 4. The low refractive index dielectric layers 10P are partially stacked on the second transparent conductive film 9b. The low refractive index dielectric layers 10P are configured to reflect the light which is emitted from the nitride light emission layer 3. The light reflective conductive film 11 is shaped to cover the low refractive index dielectric layers 10P and the second transparent conductive film 9b. The light reflective conductive film 11 is configured to reflect the light which is emitted from the nitride light emission layer 3. The barrier metal layer 14 is formed on the light reflective conductive film 11. That is to say, the LED chip of FIG. 3 has a light extracting surface in one surface in the thickness direction of the nitride light emission layer 3, and a first surface which is opposite of the light extracting surface from the nitride light emission layer 3. In addition, the LED chip is provided at its first surface with the low refractive index dielectric layers 10P. The nitride light emission layer 3 is configured to emit the light toward both the light extracting surface and the anode electrode 7. When the nitride light emission layer 3 emits the light toward the anode electrode 7, the light is reflected by the low refractive index dielectric layers 10P and the light reflective conductive film 11. The low refractive index dielectric layers 10P and the light reflective conductive film 11 are configured to reflect the light toward the light extracting surface. It is noted that the arrowed line C shown in FIG. 3B discloses one example of a path of the light which is emitted from the nitride light emission layer 3, which is taken in the low refractive index dielectric layers 10P, and which is reflected by the low refractive index dielectric layers.
The above mentioned first transparent conductive film 9a has a thickness of 2 nm to 10 nm. The first transparent conductive film 9a is made of material such as Ni, Pd, Pt, Cr, Mn, Ta, Cu, Fe, or alloy including at least one of them. The second transparent conductive film 9b is made of one of the materials selected from ITO, IZO, ZnO, In2O3 SnO2 MgxZn1-xO (x≦0.5), amorphous AlGaN, GaN, SiON. In addition, the light reflective conductive film 11 is made of material such as Ag, Al, and Rh. The anode electrode 7 is made of metal material of Au. The barrier metal layer 14 is made of material of Ti.
Each one of the low refractive index dielectric layers 10P which are mentioned above has a cross section which is perpendicular to the thickness direction of the LED chip; the cross section of the low refractive index dielectric layer 10P has a circular shape. In addition to the above, each one of the low refractive index dielectric layers 10P is disposed on the second transparent conductive film 9b such that the low refractive index dielectric layers 10P are arranged in the two dimensional array. More specifically, each one of the low refractive index dielectric layers 10P is disposed on a lattice point of a square lattice along the plane which is perpendicular to the thickness direction of the LED chip. That is, FIG. 3 discloses the LED chip which comprises a plurality of the low refractive index dielectric layers 10P; the low refractive index dielectric layers 10P is arranged along the plane in parallel with the nitride light emission layer 3; each one of the low refractive index dielectric layers 10P has an arrangement which resembles the island to be isolated from each other.
In addition to the above mentioned configuration, the low refractive index dielectric layers 10P comprise alternating layers of two kinds of the dielectric layers; the two kinds of the dielectric layers have electrical insulation properties and are different in the refractive index from each other, whereby each one of the low refractive index dielectric layer 10P has a periodic structure that the refractive index is periodically changed. The low refractive index dielectric layers 10P are made of material such as SiO2, ZrO2, TiO2, Al2O3, Si3N4, and AlN.